We shall study regulation of protein biosynthesis during embryogenesis, to gain a firmer understanding of molecular mechanisms which underlie such developmental phenomena as differentiation and growth. Our attention shall be focused on regulation at the translational level of protein synthesis because it is at this level that the protein biosynthetic machinery appears to be controlled during the initial stages of development. In particular we hope to confirm and to extend our present knowledge of the macromolecular structure of the gene for rRNA. This added information will be used to further the investigation of regulation of the synthesis and processing of rRNA the assembly of the 60S ribosomal subunits and the association of the tightly bound polysome-membrane complexes. In addition we shall complete our current characterization of the kinds of protein made on "free", loosely bound and tightly bound polysomes at the several stages of amphibian embryogenesis.